1. Field of the Invention
The present invention relates to a triangular wave generation circuit and it particularly relates to a triangular wave generation circuit which can be synchronized with an external circuitry.
2. Description of the Related Art
Pulse-width modulation techniques are widely used for inverters for converting DC voltage to AC voltage, power supply units such as a DC/DC converter for converting DC voltage to DC voltage, motor driver circuits for driving motors and the like. A pulse-width modulation is performed in a manner that error between a voltage to be controlled and a target voltage is amplified by an error amplifier and then the error voltage resulting therefrom is compared by a comparator with a periodic voltage with a triangular waveform having a certain frequency.
To generate periodic voltages of triangular waveforms used in such applications as mentioned above, analog triangular wave generation circuits as described in Patent Document 1 and Patent Document 2 are used widely. The triangular wave generation circuit charges and discharges a capacitor and alternates the charging and the discharging by comparing with two threshold values so as to generate a desired triangular wave signal.
[Patent Document 1] Japanese Patent Application Laid-Open No. 2004-72657.
[Patent Document 2] Japanese Patent Application Laid-Open No. 2001-345682.
There are cases where it is desired that triangular wave signals synchronized with each other are generated in two different semiconductor integrated circuits (hereinafter referred to as “IC” also). For instance, consider a case where two inverters are provided at both ends of a fluorescent lamp used as backlight of an LCD television and then supply drive voltages of mutually reversed phases are applied.
In the two inverters, when a phase lag occurs in triangular wave signals used in the DC/AC conversion, the phases of voltage applied to the both ends of the fluorescent lamp are not mutually reversed, thus causing an adverse effect on its emitting state. There are other occasions where the generation of triangular wave signals synchronized with an external signal is desired.